As infrared rays can be generated from a heat source even in the dark and are more permeable to smoke and fog than visible light, infrared imaging can be performed at any time of the day or night. Temperature information about an object can be obtained through infrared imaging, and therefore, has a wide range of application, such as defense fields, surveillance cameras, and fire detecting cameras.
In recent years, “uncooled infrared solid-state image sensors” that do not require cooling mechanisms have been actively developed. In an infrared solid-state image sensor of an uncooled type or a heated type, an incident infrared ray of approximately 10 μm in wavelength is converted into heat by an absorption mechanism, and the temperature change in the heat sensing unit caused by the small amount of heat is then converted into an electrical signal by a thermoelectric converting means. The uncooled infrared solid-state image sensor obtains infrared image information by reading the electrical signal.
For example, a known infrared solid-state image sensor uses silicon pn junctions that convert temperature changes into voltage changes by applying a constant forward current. Using a SOI (Silicon on Insulator) substrate as a semiconductor substrate, such infrared solid-state image sensors can be mass-produced through a silicon LSI manufacturing process. Also, a row select function is realized by taking advantage of the rectifying properties of the silicon pn junctions serving as the thermoelectric converting means, so that the pixel structures can be dramatically simplified.
In the process of manufacturing infrared solid-state image sensors, hundreds to thousands of pixels out of 640×480 pixels might turn into defective (insensitive) pixels. In such pixels (defective pixels), information obtained by the pixels as image sensors is lost. Therefore, defective pixels need to be detected in an early stage of the manufacturing process.
There is a known method of determining a pixel address to replace a defective pixel address in a short period of time. By this method, however, inspection cannot be performed on infrared sensor chips or wafers. Infrared sensor chips need to be turned into a module through packaging, and a camera board or lens needs to be attached to the module to capture an image of an object. By this method, inspection is performed in the most downstream stage of the manufacture. As a result, throughput in the manufacture becomes lower, and production costs become higher.